The invention is a device used in continuous and semicontinuous processes for the production of substantially flat material in a sheet, web or strip of materials such as paper or metals including copper, steel or aluminium. More particularly the invention is a transfer roll for use industrial processes such as in a paper machine or a rolling mill where a material is produced or processed as a strip.
In the production and processing of strip and sheet materials it is a basic requirement that a strip material is produced to a specification which typically includes at least a predetermined thickness and predetermined material properties. To achieve such predetermined requirements any mechanical forces applied to the strip during processing must be accurately controlled. A transfer roll that conveys strip material from one part of a process to another must convey the material while exerting a controlled tension or pressure that is accurately controlled and evenly distributed over the width of the roll.
A roll described in U.S. Pat. No. 3,481,194 issued in 1969 is designed as a measuring roll to measure flatness in a metal strip passing over the roll. Flatness is indirectly measured by the measuring roll with the help of a number of force sensors arranged inside the roll and against the inside of the outer cylindrical surface. The roll is notionally divided into a number of parallel zones across the width of the measuring roll and a force sensor measures a force applied by the roll to the strip in each zone. In this way the amount and distribution of force applied by the roll to the strip is known and process control techniques may be used to correct or optimise those forces to regulate properties of the strip such as, for example, tensile strength, flatness or other dimensional qualities. However, demands for increased accuracy over time means that it is difficult to measure certain forces in any one zone accurately. This is because of a tendency for a force applied in a zone of the roll to be shared with or transferred to an adjacent zone.
Transfer of force in an unintended or uncontrolled way is sometimes described as crosstalk. It is used in this description to describe uncontrolled transfer of mechanical forces between mechanically connected parts of a transfer roll.
U.S. Pat. No. 4,366,720 discloses a method of constructing a deflector roll, or a measuring roll. The roll is constructed using a series of disk-shaped sections of a cylinder, some of which are equipped with force measuring sensors. However, in general a difficulty arises with cylindrical rolls comprising such disk-shaped sections. In an industrial environment. there is a tendency for contaminants such as dirt, grease, particulate material or oxides to become trapped between neighbouring disk sections during normal use. This can give rise to a partial and unregulated transfer of force, crosstalk, between the disks, making it difficult to ensure accuracy of force distribution across the roll and of force measurement in areas distributed across the roll.
It is an object of the invention to provide a transfer roll in which an outer cylindrical skin of the transfer roll is separated into a series of cylindrical elements connected together by a mechanical connection of a known and predetermined stiffness.
It is another object of the invention to provide a transfer roll with which measurements of force taken in each cylindrical element of the roll are subject to a known and limited degree of crosstalk between elements, and a means for providing that result in the transfer roll.
Another object of the invention is to provide a method for welding together cylindrical elements to provide a transfer roll in which the cylindrical elements are mechanically connected to each other to a known and predetermined extent.
A yet another object of the invention is to provide a transfer roll in which the cylinder or cylindrical elements making up the cylinder are in a pre-stressed condition.
A further object of the invention is to provide a means for measuring a property of a strip material which measured value may be used in a monitoring, control or regulation function for the same strip material in the same or another process.
It is an object of the invention to provide a system to reduce flatness error in at least part of the length of a strip.
The invention may be summarily described as a transfer roll that carries a flat or strip material over from one device to another in a process. In particular the present invention is a transfer roll in which at least the inside surface of the cylindrical skin of the roll is wholly or partly separated into two or more cylindrical elements. By providing a means for reduced, predetermined and constant mechanical stiffness in a region of the cylinder between each cylindrical element, mechanical properties of the cylindrical skin in different parts of the overall cylinder are made dependent to a predictable degree within the operating limits of the transfer roll. First, this means that force applied by the transfer roll to a strip material may be applied evenly and with a greater accuracy than that previously available. Secondly, measurements carried out using the transfer roll are dependent to a known degree between one cylindrical element and the next. The degree of dependency due to crosstalk is known based on the predetermined mechanical stiffness and may be compensated for by calculation. This provides a consequent and decisive improvement in accuracy compared to existing transfer rolls. Consequently an error in a material property of the strip material passing over the transfer roll may be detected with greater accuracy than before. Optionally, error measurements measured with a greater accuracy than previously may subsequently used to reduce or correct such errors in the present process or another process for the same material.
The main advantage of the invention is that a strip of flat material may be processed or produced to a required property specification such as thickness or flatness with less error, and consequently less downgrading of product, scrap and waste. Such a significant reduction in errors and scrap will produce a large environmental benefit in terms of reduced use of materials and energy in the industrial processes where the transfer roll is used. The economic benefit of improved accuracy and reducing waste of materials and energy in continuous and other processes producing vast quantities of, for example, paper, board, foils, metals and plastic or synthetic materials is also great.
A method is described for providing a welded joint as a means for providing a region of predetermined and reduced stiffness between any two cylindrical elements of the transfer roll. An advantage of the method disclosed according to a best use of the present invention is that the design of the joint also acts to prevent molten material from the welded joint from entering the interior of the transfer roll. Another advantage of this method is that any small variation in depth of weld is accommodated by an advantageous allowance in thickness of an un-fused part of the element cross section. A further advantage of the welded joint is that the cylindrical elements may conveniently and separately be pre-stressed before they are joined together. Pre-stressing the cylindrical skin provides for increased accuracy of measurement of force applied by the roller to a strip.
It is also an advantage that the welded joint once made may also be made perfectly smooth on the outside surface of the transfer roll using conventional manufacturing techniques for producing metal covered rolls. Thus the outer surface is made perfectly flat and level to the specifications normally required so as not to mark or mar the surface of a web of material or a rolled strip. Such a welded joint may also be produced to so that it is seamless and complete, preventing the build up or penetration of contaminants of any sort.
A still further advantage of the invention is that the accuracy of measurement across the roll is greatly improved relative to the prior art, and so the transfer roll may be used in new applications and branches of industry where the previous limitations of accuracy made such transfer rolls and measuring rolls problematic.
Another advantage is that the transfer roll may be easily and economically retrofitted to existing processes to improve accuracy and thus reduce costs.